Electric direct heating method of heating metallic pieces



Oct. 23, 1962 'YUKIO TANAKA ELECTRIC DIRECT HEATING METHOD OF HEATING METALLIC PIECES Filed Oct. 19, 1959 INVENTOR. M9 BY United States Patent Ofiice 3,000,304 Patented Oct. 23, 1962 3,060,304 ELECTRIC DIRECT HEATING METHQD F HEATING METALLIC PECES Yukio Tanaka, Tokyo, Japan, assignor to To-a Kako Kabushiki Kaisha, Tokyo, Japan, a corporation of Japan Filed Oct. 19, 1959, Ser. No. 847,371 Claims priority, application Japan July 22, 1959 3 Claims. (Cl. 219-50) This invention rel-ates to improvements in electric heating methods of metallic pieces.

In heating metallic pieces have been conventionally used salt baths, gas furnaces, induction heating furnaces and resistance furnaces. However, a method of heating metallic pieces to be heated by self heat generation in them by directly flowing an electric current to them is lower in the cost required for the equipment, more efficient in heating and more economical than any of the above mentioned heating means.

However, according to the conventionally used method of heating metallic pieces by directly flowing an electric current in them, the electric current is made to flow by bringing brushes into contact with the metallic piece. Therefore, there is a defect in such method that sparks will be caused in the portion of contact of the brush with the metallic piece and will damage the surface of the metallic piece. There is also a defect that, when the shape of piece to be heated is irregular, the contact of the brush with the metallic piece will not be favorable and it will be diflicult to flow the electric current uniformly. Thus, such conventional method has not been well practised.

A principal object of the present invention is to provide a heating method wherein, in heating a piece by self heat generation therein by an electric current flowing thereto, the current can be made to flow without causing sparks on the surface of the piece to be heated on which the current is flowing and, even though the current is made to flow, no damage will be caused to the surface of the piece to be heated.

Another object of the present invention is to provide a method of heating pieces to be heated by relatively uniformly flowing an electric current to them, even if the shapes of pieces to be heated are irregular.

A further object of the present invention is to provide a heating method wherein the heating temperature and the portion to be heated in a piece to be heated can be freely adjusted.

According to the present invention, there is provided an electric direct heating method of metallic pieces, characterized in dipping the metallic pieces to be heated in a bed of fluidized electro-conductive carbon powder, flowing an electric current through the bed of fluidized electro-conductive powder and the pieces, and adjusting the heating temperature of the portion in the pieces by controlling the intensity of the electric current.

In the above explanation, the electro-conductive powder may be a carbon powder which can pass an electric current. In order to obtain a bed of a fluidized electroconductive powder, for example, a bottom wall made of such material which passes gases but does not pass the electro-conductive powder as a micro-porous tile plate is provided in the middle of a chamber, the electro-conductive powder is placed on the bottom wall and a gas or, for example, air under pressure is pressed in through an inlet provided in the bottom of the chamber, so that the electro-conductive powder may be fluidized. The size of the particles of the electro-conductive powder depends on the specific gravity and fluidity of the material of said powder. In the case of a carbon powder, the size of 100 to 150 meshes per inch is desirable. The gas to fluidize the electro-conductive powder depends on the volume of the chamber and the thickness and microporosity of the bottom Wall. Compressed air of about 4 to 10 kg./cm. is used. Such inert gas as nitrogen may be used in place of air.

In flowing electric current through the bed of electroconductive powder, an alternating, pulsating or direct current is used. When the fluidizing chamber containing the fluidized electro-conductive carbon powder is made of an electro-conductive material, an alternating or direct current voltage should be impressed between the fluidizing chamber and the piece to be heated, and the current intensity should be adjusted by a regulator belonging to the electric source. In such case, the current will flow into the piece through the fluidized electroconductive powder and the powder will act as an electric contact. If the chamber is made of an insulating material, the electrodes may be dipped in the fluidized electroconductive powder and the voltage may be impressed between said electrodes and the piece to be heated.

The present invention shall now be explained with reference to drawings.

FIGURE 1 is a vertically sectioned side view of an apparatus to be used in working the method of the present invention.

FIGURE 2 is a vertically sectioned principle view of an apparatus as used in working the method of continuously heating metallic wires, bars and tubes.

In FIGURE 1, 1 is a fluidizing chamber made of an electro-conductive material and 2 is a micro-porous bottom wall made of a micro-porous material such as, for example, a micro-porous tile plate and provided in the middle bottom of said fluidizing chamber. The microporous material of the bottom wall is such as passes gases but does not pass the electro-conductive powder. 3 is an inlet for introducing compressed air and provided in the fluidizing chamber. 4 is such piece to be heated as a metallic piece. 5 is an alternating, direct or pulsating current source. 6 is a regulator for adjusting the current intensity. 7 is a switch. 8* is a bed of fluidized electro conductive carbon powder.

As described above, when electro-conductive carbon powder is contained in the fluidizing chamber 1 and compressed air is pressed in through the inlet 3, the electroconductive powder will be fluidized within the fluidizing chamber. The piece 4 to be heated is dipped in the bed of the fluidized electro-conductive powder. When the switch 7 is closed so as to impress the voltage on the piece 4 to be heated and the fluidizing chamber 1, an electric current will ilow thorugh the fluidized electroconductive powder. The intensity of the current flowing to the piece to be heated is adjusted by the regulator 6.

In such case, the fluidized electro-conductive powder will be electrically charged and will therefore operate just the same as ions in a discharge tube so as to charge electricity. The contact resistance between the fluidized electro-conductive powder and the surface of the metallic piece is so high that heat will be generated mainly due to Joules heat in these parts and also somewhat by the resistance of the electro-conductive powder itself and of the piece to be heated.

If the current density of the surface portion of the piece to be heated is varied by adjusting the regulator 6, the surface-heating and through-heating of the piece to be heated will be possible. That is to say, if the current density is made lower, it will be possible to heat the whole of the piece to be heated and, if the current density is made higher, mainly the surface portion of the piece will be able to be heated.

In FIGURE 2, 11 is a fluidizing chamber made of an electro-conductive material. 12 is a micro-porous bottom wall made of a micro-porous material and provided in the middle bottom of the fluidizing chamber. 13 is an inlet for introducing compressed air and provided in the fluidizing chamber. 14 is such piece to be heated as a metallic wire. .15 is a packing attached to the side wall of the fluidizing chamber so that the metallic Wire may flow through the central part of the packing. It is necessary that the electro-conductive powder should not leak out through the clearance between the packing and the metallic wire. '16 is an alternating, pulsating or direct current source. 17 is a regulator for adjusting the current intensity. 18 is a switch.

In the apparatus shown in FIGURE 2, when such electro-conductive powder 19 as a carbon powder is contained in the fluidizing chamber 11. and compressed air is pressed in through the inlet 13, the electro-conductive powder will be fluidized within the fluidizing chamber. In case such continuous piece to be heated 14 as a metallic wire is passed in the direction indicated by the arrow while being dipped through the bed of the electroconductive powder, if the switch 18 is closed so as to impress the voltage between the piece to be heated 14 and the iiuidizing chamber 11 and the intensity of the electric current flowing to the piece to be heated is adjusted by the regulator 17, then the electric current will flow to the piece through the fluidized electro-conductive powder from the fluidizing chamber walls so that the piece may be heated.

In the heating method shown in FIGURE 1, it is possible to heat the piece to be heated in a rotating state while rotating the piece around an axis provided on said piece as a centre. Further, instead of using the fluidizing chamber as one of the electrodes, it is possible to provide one or more electrodes in the bed of the fluidized electroconductive powder and to connect the electric source thereto.

It is possible by expanding the heating method shown in FIGURE 2 to arrange two fluidizing chambers containing such electro-conductive powder so as to pass such continuous piece to be heated as a metallic wire through the side walls of one of the fluidizing chambers and thenhating current to the piece to be heated and heat it. It is further possible by adjusting the current intensity to freely adjust the heating temperature so as to heat either the whole or the surface portion of the piece to be heated. According to my experiments, in such continuously heating method as is shown in FIGURE 2, when a carbon: powder of about 'meshes per inchwas used-for the: electro-conductive powder, a micro-porous tile plate 30! mm. thick was used for the micro-porous bottom walli and compressed air was fed in under a pressure of about. 7 kg/crn. through the inlet made in the bottom, of the. fluidizing chamber so as to fluidize the carbon powder,.. the state of the fluidizedpowder was 30%. higher than. when no fluidization was caused. When an iron wire 1 mm. in diameter was passed at a speed it of jabout l0 m./rnin. over a surface area of about 100. mm. through: such atmosphere while a single-phase alternating current. of 100 amperes at 50 volts was being flowed between. the fluidizing chamber and the iron wire, the wire could. be heated to about 600 C.

The heating method according to the present invention: can be extensively applied to heating or tempering wheels. and to continuously annealing piano wires, copper rods brass plates and so forth.

What is claimed is:

1. An electric direct method of heating electrically conductive metallic pieces, characterized in dipping me-- tallic pieces to be heated in a bed of fluidized electro-- conductive carbon powder rotating the pieces around an. axis, flowing an electric current through the. bed of fluidized carbon powder to the piece, and adjusting the heating temperature of the piece being heated by controlling the current density at the surface of said metallic piece.

2. An electric direct method of heating relatively long metallic pieces, of uniform cross-section, including metal" wires, which are electrically conductive, characterizedin maintaining a bed of carbon powder in fluidized state; passing the metallic piece through the bed of fluidized carbon powder, flowing an electric current through the bed of fluidized electro-conductive carbon powder to the. metallic piece, and adjusting the heating temperature of the metallic piece undergoing heating by control'lingthei current density of the electric current at the surface of the metallic piece being heated.

3. Method defined in claim 2, further characterizedin that a plurality of metal wires, arranged side by side, are passed through said bed of fluidized carbon powder whilst electric current simultaneously is passed through said bed and to said wires.

References Cited in the file of this patent UNITED STATES PATENTS 441,401 Dewey Nov. 25, 1890 749,418 Acheson Jan. 12, 1904 FOREIGN PATENTS 689,165 France May 26,1930

801,653 Great Britain Sept. 17, 1958- UNITED STATES PATENT 0FFICE CERTIFICATE OF CORRECTION Patent No. 3,060,304 October 23 1962 Yukio Tanaka It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 4, line 26, after "fluidized" insert electroconductive Signed and sealed this 19th day of March 1963.

(SEAL) Attest:

DAVID L. LADD Commissioner of Patents ESTON G, JOHNSON Attesting Officer UNITED STATES PATENT UFIPICE CERTIFICATE OF CORRECTION Patent No. 3,060,304 October 23, 1962 Yukio Tanaka It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 4, line 26, after "fluidized" insert electro conductive Signed and sealed this 19th day of March 1963.,

SEAL fittest:

DAVID L. LADD Commissioner of Patents ESTON Ga JOHNSON Attesting Officer 

1. AN ELECTRIC DIRECT METHOD OF HEATING ELECTRICALLY CONDUCTIVE METALLIC PIECES, CHARACTERIZED IN DIPPING METALLIC PIECES TO BE HEATED IN A BED OF FLUIDIZED ELECTROCONDUCTIVE CARBON POWDER ROTATING THE PIECES AROUND AN AXIS, FLOWING AN ELECTRIC CURRENT THROUGH THE BED OF FLUIDIZED CARBON POWDER TO THE PIECE, AND ADJUSTING THE HEATING TEMPERATURE OF THE PIECE BEING HEATED BY CONTROLLING THE CURRENT DENSITY AT THE SURFACE OF SAID METALLIC PIECE. 